This proposal will investigate the physiological role of the Clara cell secretory protein (CCSP) within the lung. CCSP is one of the most abundant secretory proteins of Clara cells and is present in large quantities with the lumen of airways. CCSP has been indirectly implicated as an important factor in morbidity associated with lung toxicity following exposure to environmental pollutants. Biochemical properties of purified CCSP are suggestive of a multifunctional molecule that may be important for protection of the pulmonary epithelium from cytotoxic chemicals and/or control of inflammation. To identify roles for CCSP within the murine lung, a model of CCSP deficiency will be generated in which the gene encoding CCSP will be interrupted within the murine germline by insertional mutagenesis in embryonic stem cells. The genetic modification will be propagated through the germline of chimeric mice for the establishment of stable CCSP deficient mouse lines (CCSP). Homozygous CCSP mice will be evaluated for the presence of functional or developmental aberrations within the lung that result from CCSP deficiency. The involvement of CCSP in the processes of xenobiotic metabolism and inflammatory control within the lung will be evaluated using established models of chemically induced cytotoxicity, and hyperoxia induced inflammation, to probe the responsiveness of wild-type and CCSP mice to pulmonary insult. The response of mice to pulmonary insult will be characterized by histological evaluation with defined morphological criteria to document differences in pulmonary epithelial cell injury and inflammation between wild-type and CCSP mice. These studies may identify otherwise silent phenotypic traits of CCSP mice indicative of the role of CCSP within the lung. Temporal and spatial requirements for CCSP function will be investigated using hybrid lung- specific promoter-CCSP genes and transgenesis to achieve partial complementation and overexpression of CCSP within defined pulmonary epithelial cell populations of CCSP and wild-type mice. Completion of these aims will identify physiological mechanisms involved in important injury processes that accompany exposure to environmental pollutants. This may provide insights for development of new strategies to avoid short term lung injury and the long term consequences of exposure to potentially mutagenic compounds.